Automatic telephone switch



Nov. 30, 1937. lR. G. RlcHARDsoN 29100517 AUTOMATIC TELEPHONE SWITCH 3Sheets-Sheet 2 Filed May l, 1936 INVENTOR. PODNE-Y G. IQICHARDSONATTORNEY.

NOV. 30, 1937. R RgCg-zARDgQN 2,19%5117 AUTOMATIC TBLEPHONE swITCH FiledMay 1, 1936 3 Sheets-Sheet 5 FINDER INVENTOR. RODNEY G. DICHAIQDSONATTORNEY.

Patented Nov. 30, 1937 UNITED STATES PATENT OFFICE AUTOMATIC TELEPHONESWITCH Delaware Application May 1, 1936, Serial No. 77,361

15 Claims.

The present invention relates in general to automatic telephone systems,and more in particular to the Strowger type of system using vertical androtary switches. The object of the invention, generally speaking, is toreduce the cost of such systems.

A major item infiuencing the cost of the Strowger system is the multiplebanks. Although efforts have been made to improve manufacturing methodsso as to make the banks less expensive, the economics effected have notbeen great, and the present invention therefore proceeds along differentlines. In brief, the saving is accomplished by arranging matters so thattwo groups of switches may use the same set of multiple banks. Thisresults in reducing the number of banks in an exchange by one half andalso saves a considerable number of multiple cables that are otherwiserequired.

The invention Will be described hereinafter With reference to theaccompanying drawings, in which- Fig. 1 is a front view showing parts ofa connector switch and a finder switch using the same banks;

Fig. 2 is a side view of the same parts as shown in Fig. 1;

Fig. 3 is a section on the line 3--3, Fg. 1;

Fig. 4 is a section through one bank on the line 4-4, Fig 3;

Figs. 5 and 6 are details of the guiding and supporting means for thefinder wipers;

Fig. 7 shows a modified arrangement for selectors; and

Fig 8 is a circuit diagram of a link circuit comprisng a connectorswitch and a finder switch.

Referring to the drawings, the reference character Il] indicates a partof the frame of a Strowger connector and Il indicates part of the frameof a Strowger finder. These switches are of well known mechanicalconstruction and hence are not shown, except for parts of the frames andthe ends of the shafts carrying the wipers. In a one-hundred lineswitchboard there may be ten connectors mounted one above the Vother onsuitable uprights and ten nders similarly mounted, making two verticalrows of Switches. These two rows are spaced apart and between them is a50 single set of multiple banks, which are used in common by theconnectors and nders. Since the switches are mounted with their shaftsin a horizont-al position gravity cannot be used for restoring purposesand each switch is provided 55 with restoring mechanism of the typeshown in the` pending application of Mahoney, S. N. 18,774, filed April29, 1935.

Between frames IU and l l extend two bank rods |2 and 13, on which aremounted in the usual manner two banks 14 and l5. These banks are 5 inpart indicated diagrammatically in Figs. 1 and 2, but are shown indetail in Figs. 3 and 4. They are of the usual construction, except formodifications that Will be explained. The banks shown are multipled withsimilar banks in a 10 vertical direction.

The shaft IB of the connector carries two pairs of wipers I'l l8 and|9-20, which may be of the usual construction. In the so-called verticalmovement of the connector the shaft 16 is moved 15 step by step in ahorizontal direction to the left and thus the wipers may be positionedopposite any desired level of bank contacts. In the rotary movement ofthe connector the shaft is rotated step by step in a clockwisedirection, Fig. 3, and 20 the wipers are thus positioned on any desiredset of contacts in the selected level. These operations are wellunderstood.

The finder shaft 34 is in axial alignment with the connector shaft 16and is operated in pre- 25 cisely the same manner, except that since thetwo shafts point in opposite directions the directions of movement areopposite With respect to the bank. That is, the finder shaft moves tothe right as seen in Fig. 1 during the vertical movement of 30 theswitch and the wipers rotate in a counterclockwise direction as seen inFig. 3.

There are two pairs of finder wipers 23-24 and 25-26. These wipers arecurved in shape to conform to the shape of the bank, as seen in Fig. 3.35 The wipers are mounted as shown in Fig. 1 on a wiper carriage 22which may be of right angle section for the sake of lightness andrigidity. This wiper carriage is in turn supported on a member 2! whichis secured to shaft 34. 40

Due to the length of the finder wipers it is desirable to providesupporting means for the ends, as otherwise vibration would be apt tooccur during the vertlcal movement and the wipers might not enter thebanks properly on the ensuing rotary movement. To avoid any diflicultyonthis account, the arrangement about to be described is provided. On theshaft 34 there is mounted an arm 26, as shown in Fig. 1, which partakesin the vertical or longitudinal movement of the shaft but not in therotary movement. The arm 26 carries a horizontal member 21, also seen inFig.

1, and more in detail in Fig. 5. The right-hand clamping member 28 ofbank H is made With an extension 29, Figs. 1 and 6, which is bent asshown in Fig. 1 and les parallel to the member 21. The latter has a pinor stud 33 which lies in the slot 36 of extension 29. It Will be seenthat with this arrangement the member 21 will move longitudinally to theright during the primary movement of shaft 34, but when the shaft isrotated the member v27 will remain stationary due to the stud 33engaging the side of slot 30. The member 21 carries two insulated pins3! and 32 which lie between the wipers of wiper pairs 2% 24 and 25 26,respectively, and against Which the wipers are tensioned. It will beseen that the pins 31 and 32 serve to steady the wipersand preventvibration thereof during the primary movement of the finder and insurethat the wipers will enter the banks properly at the beginning of therotary movement. i i i The clamping member 35 of bank 14 has anextension 36 and there is a similar extension on' the clamping member 31of bank 15. To these extensions there is secured a member 38 on Which ismounted the usual vertical bank 39. This bank 39 comprises the leveltest Contacts for the finder. The level test wiper 40 is mounted on abracket M which is secured to the carriage 22. i

The banks are of the Vusual construction except for the modificationsrequired to adapt them for use by two sets of wipers simultaneously. Tothis end the bank Contacts are made somewhat longer than in the standardbank, and the wipers H-ZG of the connector, which operate on the bankcontactsclose to the ends thereof, are made slightly shorter than usual.This leaves a portion of each contact set outside the arcs described bythe connector wipers l'-l-ZU which can be engaged by the finder wipers23-28. It Will be seen, therefore, that although the finder andVconnector use the same banks the connector wipers and finder wipers maybe operated entirely independent of each other without interference.That is, the finder wipers may be positioned on any desired Set ofVContacts and while the finder remains in operated position theVconnector wipers may be positioned on any desired set of Contacts, evenon the same set that is engaged by the finder wipers.

i Fig. 4 shows the construction of the bank and also shows the relativeposition of a pair of connectorwipers and a pair of finder wipers whenengaging the same pair of contacts. It may be pointed out that theinsulators, such as 45 and 46, extend within the arc described by theouter edge of finder wipers such as 23, as is shown clearly in Figs. 3and 4. The reason for thisconstruction is to obviate any danger ofaccidental touching of Contacts by the finder wipers. These wipers arerather long and if not perfectly adjusted there might be some danger oftouching other'contacts than the ones selected, particularly at timeswhen the wipersare rotated far into the banks. V' i Referring now toFig. 8 an explanation will be made of the operation of a system in whichthe nvention is applied. It will be assumed that the system comprisesone hundred subscribersf lines and that connections areestablished bymeans of finderconnector links of which one is shown in the drawings.Two subscribers' stations A and B are also shown, with their associatedlines and linecircuits. The numbering of the subscribers' lines is, ofcourse, determined by considering the banks from the standpoint of theconnector wipers, as the connector is the switch which is directivelycontrolled by'digit impulses in accordance'with called numbers. The bankcontact sets shown in the drawings are the first COIlfit Sets of the tenlevels, that is, the first contact sets engaged by the connector wipersin their rotary motion. Now, the line of station A is connected to thefirst set of contacts in the sixth level, the levels being numbered intheir order of access from the connector wipers, and the line of stationB is connected to the first set of contacts in the eighth level. Hencethe telephone number of station A is GI and the number of station B is lIt will now be assumed that the subscriber at Station A desires to callthe subscriber at Station B. Upon the removal o-f the receiver atstation A a bridge is closed across the line in the usual manner, whichoperates the line relay 58. On energizing, the line relay places a lowresistance shunt Varound the cut-off relay 5! and 52, which has theeffect ofrmarking the line as calling in the banks of the finders suchas F, and at 53 grounds the group .or level start conductcr IH. Thelatter operation places a ground on the level test contact ll2 andoperates the common start re lay Hil. i

Upon energizing,rrelay HG closes the finder start circuit which, on theassumption that the link circuit shown in the drawings is idle, extendsthrough to the start relay IM of the finder F.

The circuit extends from ground by way of iil,

IZZ, and winding of relay le! to battery. On energizing, relay lfllconnects up' the level test wiper 40 at IZI, grounds therelease trunkconductor' 132 at 120, and closes a circuit for the vertical magnet IMat HS. The latter circuit extends from ground by way of HB, lie, lz,:26, and winding of magnet Hill to battery. Upon energizing, magnet IMoperates the finder shaft carrying wipers 23-25 one step, the directionof movement being downward as indicated in the circuit drawing, Fig. 8,and to the right as seen in Fig. l. The vertical magnet also closes acircuit for the interrupter relay lll2. On energizing, the interrupterrelay closes the level test circuit through at l25, and at lZll breaksthe circuit of the vertical magnet. The vertical magnet accordinglydeenergizes'and breaks the circuit, of the interrupter relay, whichthereupon falls back and again closes the vertical magnetV circuit. ItWill be seen, therefore, that the vertical magnet and interrupter relayoperate alternately, the former advancing the finder shaft and wipersstep by step past the levels 0, 9, 8, 7, ete.

On the fifth step Vthe wipers will be moved opposite the sixth level ofbank Contacts, and the level test wiper @30 will be brought intoengagement with the level test contact I! 2. When the interrupter relayN32 energizes, therefore, following the fifth operation of the verticalmagnet, a circuit will be completed for the level test relay l. Thiscircuit includes the lower winding of the interrupter relay N32,thus'preventing it from falling back for the time being. On energizing,relay N33 transfers the- Operating circuit from the vertical magnet HMto the rotary magnet l at l26, at l2'i prepares a circuit for the linetest or switch-through relay! ili), and closes Va locking circuit foritself at l28. At the same time that the looking circuit of relay Hl isclosed at lZ, the initial energizing circuit o-f this relay is brokenand accordingly the interrupter relay lilZ is permitted to fall back.The deenergization of the interrupter relay at this time closes acircuit for the rotary magnet i05 at l24.

The finder F now begins to operate in its rotary movement, moving thewipers 23-25 in onto the bank Contacts of the sixth level in search ofthe callingline. The rotary magnet l and interrupter relay 102cooperate' during the rotary movement the same as the vertical magnetand interrupter relay did during the vertical movement. The test relayI00 is marginal and will not operate in series with cut-off relays suchas 5 I, as these relays are of relatively high resistance. The relay I00 Will, however, operate in series with any cut-off relay which hasbeen shunted by a resistance through the operation of the associatedline relay. It follows, therefore, that the finder continues to rotateits wipers step by step until ten consecutive steps have been taken,bringing the wipers 23-25 into engagement with the first set of contactsin the sixth level. This is the set of Contacts in which the line ofstation A terminates, and since the line is now in oalling condition,test contact II3 will be found to be marked with a heavy batterypotential, due to the shunting of cut-off relay 5I at 52, as previouslyexplained. It follows that when the test wiper 25 engages test contactIi3 test relay I00 Will be energized, the circuit extending from groundat [21 by way of the lower winding of relay Iilil, test wiper 25, testcontact I I3, and thence to battery through the cut-off relay 5I and theresistance connected in parallel therewith. On energizing, relay [00stopsthe operation of the rotary magnet by opening the Operating circuitat I IB, locks itself to the release trunk conductor at I I G, connectsthe release trunk conductor through to test wiper 25-at i il, breaks thecircuit of level test relay I03 at II5, opens the circuit of start relayI OI at I22, and closesr through the heavy talking conductors of thelink to the line wipers 23 and 24. By the latter operation the callingline is extended through over wipers 23 and 24 and link talkingconductors I3I and I3-3 to the line relay 55 of the connector C. Onenergizing, the line relay closes a circuit for the slow-acting releaserelay 56 at 66. The release relay accordingly energizes and grounds therelease trunk conductor I32 at 61. When the circuit of the start relay IGI is broken at I22 it falls back, but is sufliciently slow-acting sothat ground is not removed from the release trunk condflctor at IZSuntil it has been connected at 61. The deenergization of relay IOIprepares a circuit for the release magnet I 06 at II9 and also transfersthe start circuit to the next finder at I23. The deenergization of relayN53 is of no consequence at this time.

When the test circuit is closed through the lower winding of the testrelay I00, cut-off relay 5I energizes in series with the test relay andis subsequently maintained energized by ground on the release trunkoonductor via I I'l and the test wiper 25. On energizing, relay 5Iclears the line of its normal battery and ground connections, resultingin the deenergizing of the line relay 50. This relay removes theresistance from in shunt of cut-off relay 5I, and also breaks thestarting circuit at 53. Relay 51 energizes promptly and line relay 50falls back quickly so that the common start relay IIO will bedeenergized in time to prevent the starting of another finder upon thetransfer of the start circuit by the deenergization of start relay I0l.

The calling line has now been extended to the connector C and the linkis ready for the calling subscriber to start dialling the number of thecalled subscriber.

When the calling device is operated in accordance with the first digit 8of the called number, eight interruptions are produced in the circuit ofline relay 55, and this relay accordingly deenergizes eight times,transmitting eight impulses to the vertical magnet 63 in series with thechange-over relay 57. The vertical magnet responds to these impulses andoperates the connector shaft eight steps in an upward direction as seenin Fig. 8, and to the left as seen in Fig. 1. The ofi-normal springs ONare shifted on the first step of the shaft, but the Operating circuit ofthe vertical magnet is maintained throughout the series of impulses bychange-over relay 51, which energizes on the first impulse of thevertical magnet and stays energized until the series is finished.

When the impulses for the first digit 8 have all been transmitted thechange-over relay 51 falls back and transfers the Operating circuit tothe rotary magnet 64. The subscriber may now dial the second digit 1 ofthe called number. The line relay 55 accordingly has its circuitinterrupted once, and falls back once to deliver a single impulse to therotary magnet 64. On energizing responsive to this impulse the rotarymagnet rotates the shaft of the connector and brings the wipers I'I-ISinto engagement with the first set of Contacts in the eighth level,being the set of Contacts in which the line of station B is terminated.The slow-acting relay 50 is operated in parallel with the rotary magnetand closes a circuit for the slow-acting relay GI. These two relays,therefore, are energizecl throughout the rotary movement of the switch,whether one or more rotary steps are taken. In energized position relay60 connects the test Wiper I9 with the upper winding of the busy testrelay 59 by way of 'iQ and "II, and thus when the wiper I9 is broughtinto engagement with test contact II4 of the called line a test is madeto ascertain if it is busy or idle.

The test contact II4 may have either one of two busy potentials on it.One is a ground potenf tial, which is the potential maintained on thetest contact of the line throughout the time it is busy except for ashort period when the line is calling extending from the time thereceiver is raised up to the time the line is located by a finder. Forinstance, during the explanation of the call made from station A it waspointed out how a heavy battery potential Was applied to the testcontact I I3 by the line relay 50. This potential remained on thecontact until the line Was found, when it Was replaced by a groundpotential upon the energizng of the test relay I00 of the finder. Theconnector C first tests for a ground potential. Assuming that there isground potential on test contact i 54, the busy test relay 59 Will beenergized in an obvious manner, and when slow-acting relay l falls backat the end of the rotary movement the relay 59 will become locked over acircuit which extends from ground at 58 by way of 76, 69, "II, and theupper winding of relay 55 to battery. In energized position relay 55opens the Operating circuit of the rotary magnet and connects a busytone circuit to the calling line. This notifies the calling party thatthe desired line is busy and he will hang up his receiver.

It will be assumed now that when the test contact IM is tested forground potential no ground potential is found and accordingly the busytest relay 59 will not energize. When relay 50 falls back at the end ofthe rotary movement, therefore, relay 50 not having energized, anothertest circuit is completed over which the test contact lI4 is tested fora heavy battery potential, which will be present if the associated lineis calling Vin series with cut-off relay BI' alone.

and Vhas not been located by a finder switch. This second test circuitextends from test wiper IS by way of'lO, 12, lower winding of busy testrelay 59, 76,' and 68 to ground. Relay 59 is marginal and will notoperate in the above circuit unless a heavy battery potential is foundon test contact IM. That is, relay 59 Vwill not operate Assuming,however, that station B is calling, the line relay 50' will be inenergized position and cut-off relay l' will be shunted by a resistance.Under this condition the requisite heavy battery potential will bepresent on test contact ll4, and test relay 59 will operate. Onenergizing, relay 59 locks itself at 69 and breaks the test circuit at16. Otherwise the test relay functions as before and gives the callingsubscriber a busy signal.

It will be assumed now that the line of station B is idle when called.Under these circumstances there will be no busy potential, neitherground nor battery, on the test contact I hi, and test relay 59 will notenergize in either of the two successive tests Vthat are made. Thedeenergization of relay 60 is followed after a short interval by thedeenergization of relay ESI, which opens its Contacts 12 and thusremoves'the short circuit from the lower winding of sWitching-throughrelay 62. Relay 62 is adapted to energize in series with a cut-off relaysuch as l', and accordingly pulls up over a circuit which extends fromground at 58 by way of 16, lower winding of 58, lower winding of 52,lil, test wiper l9, test contact Hil, and winding of cut-off relay l' tobattery. The cutoif relay 51' energizes in series with relay 62 andclears the line of station B in the usual manner.

At connector C the energization of relay 62 connects up the two linewipers Il and IS in the usual manner. Relay 62 also locks itself at 14,places a ground on test wiper IB at 13, and breaks the circuit of therotary magnet Gll at 15.

V V Upon the operation of the switching-through relay 52, as previouslyexplained, the called lineV is signalled in the usual manner, ringingcurrent being transmitted through the lower winding ofV ring-cut-offrelay 53. When the called party responds by removing his receiver therring-cut off relay 58 operates and locks itself to ground at 57. Thering-cut-oif relay also opens the ringing circuit and completes thetalking circuit through the connector. The calling and calledsubscribers are now connected for conversation. Station A is suppliedwith transmitter battery through the winding of relay 55, While stationB is supplied with transmitter battery through the winding of the backbridge relay 50. I The latter 1 may be arranged to reverse the directionof current flow in the calling line as shown in the drawings.

When thesubscribers are through talking they will hang up theirreceivers. The release of the connection is brought about by thereplacement of the receiver at the calling Station A, which opens thebridge across the calling line and breaks the circuit of the line relay55. On falling back,

' relay 55 opens the circuit of the release relay and When this relaydeenergizes a circuit is closed for the connector release magnet 55.Release magnet accordingly operates and restores the connector in theusual manner. tion of relay also removes ground from the release trunkconductor 132, which breaks the looking circuits of relays 58 andV 52and allows them to deenergize. At the finder F theremoval of ground fromthe release trunk conductor 32 allowsrelay i Vto fall back, .whereuponThe deenergizaa circuit is closed for the. release magnet l06. Magnet lenergizes and restores the finder in the usual manner. The removal ofground from the release trunk conductor 132 also permits the cut-offrelay 51 to fall back, restoring the calling line to normal condition.Cut-oif relay 55' on the called line is, of course, allowed todeenergize when relay 62 of theconnector falis back. Thus the equipmentinvolved in the connection is restored to normal.

The described system may be readily converted to a two-hundred linesystem by suitably lengthening the bank rods such as |2 and 13 and byadding another bank for each paired finder and connector. Each switch isalso provided with another pair of wipers. The wipers such as 20 and 26,not used in the one-hundred line system shown in Fig. 8, would then' beused as the test wipers for the second hundred lines.V

The circuit arrangements of two-hundred line nders and connectors arewell known and hence need not be explained.

The principles of the invention are also applicable to selectors, andtherefore the invention can be used in systems of any size. Consideringa given group of selectors, for example, half of them may be mountedside by side on a shelf in the usual up-right or vertical position,while the other half are mounted on a similar shelf immediately belowwith a common set of banks between the two shelves. The switches beingmounted vertically, the shafts are restored by gravity. The selectors ofthe upper shelf are in all respects standard selectors, except that thewipers should be slightly shorter than usual, as described inconnectionV with the wipers Il-20, Fig. l. The selectors of the lowershelf are similar to standard switches but are modified in" The shaftsdo not extendV the following manner. belowthe switches as is the usualcase, but extend upward toward the common banks and each shaftis'equipped with a special set of curved wipers mounted on an offsetwiper carriage as shown in Fig. 1. In addition, the switches arearranged to rotate their shafts in the opposite direction as comparedwith the switches 'in the upper shelf. This amounts to a mere reversalof the parts having to do with the rotary movement.

The arrangement of the shafts and wipers of two selectors one in theupper shelf and one immediately below in the lower shelf is depicteddiagrammatically in Fig. 7. This drawing indicates two banks 20! and 202supported on bank rods 203 and 2%4 which 'extend between the switchframes. The frame of the lower switch is, of course, arranged to receivethe bank rods at the top of the frame instead of at the bottom. Theshaft 205 of the upper selector carries two pairs of wipers 201 and 208and has vertical and rotary movements in the directions indicated by thearrows. The shaft 205 of the lower selector carries twoV sets of wipers2139 and ZIG, which are similar to the wipers mounted on shaft 315 in 1.shaft 206 has a vertical movement in the same same order, and bothswitches can be operated i numerically to select the sameV trunk groups,as is essential. In the drawing the shaft 206 is shown partiallyoperated as regards its vertical position, so that the wipers 209-210will not Vobscure the wipers on shaft 205. It will be understood thatnormally all wipers stand just below the first bank level.

Another plan that could be adopted is to reverse the curved wipers. Forinstance, and referring to Fig. 3, wipers such as 23 and the wipercarrage 22 could be so constructed that the wiper tips normally lie justoutside the tips of wipers such as Il and rotate in on the banks in thesame direction. If this scheme is applied to the selectors indicated inFig. '7, the Shaft 206 would be arranged to rotate in the oppositedirection from the direction shown by the arro-w, or in the samedirection as shaft 205. This arrangement would have the advantage thatthe switch operating mechanisms would be the same, instead of half theselectors having clockwise rotary movements and half counter-clockwiserotary movements. On the other hand, the selector arrangement firstdescribed has the advantage that half of the selectors search over trunkgroups in the opposite directon from that in which such groups aresearched by the other half, which effects a distribution of trafiic totrunk groups from the same group of Switches without any slip in themultiple between Switches.

Either of the foregoing selector arrangements can, of course, be appliedto groups of finders and connectors arranged in pairs as hereinbeforedescribed. If the second arrangement is employed, in which the wipers ofboth Switches of a pair move in the same direction as regards bothvertical and rotary motions, each pair of Switches need not comprise afinder and a connector, but the connectors may be paired with each otherand likewise the finders. Thus in an arrangement of ten connectors andten finders for a onehundred line group, the Switches could be mountedon two spaced shelves with the banks between as descrimbed for selectorsand the first five Switches in each Shelf would be connectors, while thelast five Switches in each shelf would be finders.

What is claimed is:

1. In combination, two vertical and rotary motion Switches positionedwith their shafts in alignment, a set of arcuate banks positionedconcentric with the axis of said shafts, and wipers on each shaftadapted to be positioned on any set of contacts in said banks withoutinterfering with the wipers on the other shaft.

2. In combination, a bank comprising arc Shaped rows of contacts, twoSwitches having primary row Selecting motion and secondary contactSelecting motion, and wipers for said Switches having common access tosaid bank.

3. In combination, two spaced rows of Switches, said Switches havingshafts extending from the opposite Switch rows into the space betweenthem, a row of multiple banks mounted in said space, and wipers on saidshafts having common access to said banks.

4. In combination, a bank comprising contacts arranged in rows, a switchhaving access to said bank and having primary movement to select a rowand a secondary movement to select a contact in a selected row, and asecond switch having access to said bank and having primary andsecondary movements which are opposite in direction to the correspondingmovements of said first switch with respect to Said bank, whereby thedistances moved by the second switch to reach any contact arerepresented by values which are complementary to the values representingthe distances moved by the first switch to reach the contact.

5. In an automatic switch, a rotary Shaft, a bank having contactsdisposed on the circumference of a circle the center of which lies onthe rotation axis of said shaft, an arc shaped wiper positioned on adifferent part of the same circumference on which said contacts aredisposed, said wiper having a part at one end adapted to engage saidcontacts successively, and a radial member connected between the otherend of said \Viper and Said Shaft.

6. In an automatic switch, an arcuate bank, an arcuate wiper Subtendingthe Same angle as .Said bank, means for supporting said bank and wiperon a common center, and means for producing relative angular motionbetween the bank and wiper about said center.

7. In combination, two separate and independently operabe Switchesmounted in alinement with a space between them, a bank of individualbank contacts mounted in the Space between the alined Switches, andwipers for each switch adapted to be positioned on any of saidindividual bank contacts of said bank without interfering with thewipers of the other Switch.

8. In combination, two separate and independently operable Switchesmounted in alinement with a space between them, a shaft for each Switchextending into the Space between the alined Switches, a bank common toonly said two Switches mounted in the space between said alinedSwitches, said bank comprising a plurality of individual bank contactsarranged in rows, and wipers on each shaft adapted to be positioned onany of said individual bank contacts of said bank without interferingwith the wipers of .the other switch.

9. In combination, two separate and independently operable Switches, abank common to only said two Switches, Said bank comprising a pluralityof individual bank contacts arranged in a plurality of rows, wipers onthe first switch operable in a given direction to successively engageany of said individual bank contacts in said bank, and wipers on theSecond switch operable in a reverse direction to the first Switch wipersto successively engage said same individual bank contacts in reverseorder without interfering with the wipers of said first switch.

10. In combination, two separate and independently operable Switches, abank common to only said two Switches, said bank comprising a pluralityof individual bank contacts arranged in a plurality of rows, and wipersfor each Switch operable in directons reverse to each other tosuccessively engage the same individual bank contacts but in reverseorder without interfering with each other in case of concurrentOperations thereof.

11. In combination, two separate and independently operable Switches, abank common to only said two Svvitches, said bank comprising a pluralityof individual contacts arranged in a plurality of rows, wipers on thefirst Switch adapted to be positioned on any of Said individual bankcontacts in said bank, and wipers on the Second switch adapted to bepositioned on said same individual bank contacts in said bank as thewipers of the first switch without interference therefrom.

12. In combination, two separate and independently operable Switches, abank common to only Said two Switches, Said bank comprising a pluralityof individual bank contacts arranged in a plurality of rows, and wipersfor each switch 'the other shaft.

14. In combination, a bank comprising arc shaped rows of individualcontacts, two Switches having primary row Selecting motions indirections reverse to each other and secondary con- Vadapted to' engageany of said individual bank 'tact Selecting motions in'directions'reverse to each other, and wipers for said Switches havingcommon access to'said individual bank contacts.

15. In combination, two switches mounted in.

